The present invention relates to information recording apparatus for recording data on a recording medium in encrypted form and information reproducing apparatus for reproducing data recorded on a recording medium, as well as programs to be executed by a computer for recording and/or reproducing data to and from a recording medium.
In recent years, it has been widely popular to deliver various digital content, such as music and image content, via the Internet and various other communication networks. Under such an environment, any interested user can purchase or acquire desired content (e.g., music piece data) by downloading, via such a communication network, the desired content from information provider that supply music content and the like. Further, with recent advancement of data compression techniques, it is possible to record content, acquired via the Internet, on a physical medium (recording medium) with high quality. Under such circumstances and from the viewpoints of copyright protection etc., there is a great demand today for techniques to effectively prevent unfair or unauthorized copying and use of digital content.
As a technique for preventing such unfair or unauthorized copying and use of digital content, it has been known to employ a recording medium having a unique medium ID imparted thereto, such as Smart Media (registered trademark). More specifically, it has been known that data of downloaded content to be recorded on a recording medium are encrypted by use of the medium ID unique to the recording medium, and, in reproduction of the recorded content, the encrypted data of the content are decrypted using the unique medium ID of the recording medium. In this case, if downloaded to the recording medium in a fair (rightful) manner, the content can be appropriately decrypted and reproduced from the recording medium, because the medium ID used for decrypting the content coincides with the unique medium ID used for encrypting the content. If, on the other hand, particular content is first downloaded to the recording medium in a fair (rightful) manner and then unfairly (unrightfully) copied from the recording medium to another recording medium, then the data of the content read out from the other recording medium can not be appropriately decrypted, because the medium ID unique to the other recording medium is different from the unique medium ID used for encrypting the content; thus, the content can not be reproduced from the other recording medium. In this way, the known technique can prevent unfair copying of the content.
However, the aforementioned conventionally-known technique is disadvantageous in that, before all recorded data of content to be reproduced from a given recording medium have been decrypted, it can not determine whether the data are fairly-recorded data, i.e. reproducible (more specifically, reproduction-permissible) data. Because decrypting the data is quite time-consuming, the conventionally-known technique would lack processing quickness.